Methods and apparatus for manufacturing asphaltic paving composition are well known. Typically, virgin aggregate is heated and dried in a rotating drum, and then liquid asphalt is mixed with the heated aggregate, typically in the proportion of 5% to 6% asphalt by weight, to form the paving composition. This mixing can be done in the lower end of the same rotating drum in a zone removed from the heat source, or the aggregate and asphalt can be mixed in a separate mixing apparatus. Optionally, recycled asphalt roadway material can be mixed with the aggregate in a zone of the drum which is hot enough to melt the asphalt in the recycled roadway material but not so hot as to cause excessive smoking.
Each year, there are approximately 80,000,000 squares of roofing shingles produced. A square is 100 square feet of shingles and contains approximately 80 shingles weighing a total of approximately 235 pounds. Typically, shingles manufactured prior to 1980 consist of 25% granular material and 75% binder. The binder consists of 70% asphalt and 30% limestone filler, resulting in a total composition of 52.5% asphalt. Shingles manufactured subsequent to 1980 typically consist of 25% asphalt, 25% fiberglass, and 50% granular/filler material.
Approximately 60% of roofing shingles are used for new construction and 40% for old construction. A building can be re-roofed three times prior to having to tear the old shingles off, but when the shingles are removed, all three layers are removed. Therefore, eventually as much as 40% of the shingles produced will be disposed of. Accordingly, with 80,000,000 squares of shingles being produced each year, even with the newer shingles containing only 25% asphalt, 2,275,000 tons of liquid asphalt per year are being disposed of.
In addition to disposing of old shingles, there is considerable waste associated with the manufacture of new shingles. Each shingle has three tabs cut out which measure one-quarter inch by 5". This represents approximately 21/2% of each shingle which is cut out as tabs. Based upon the annual output of new shingles, approximately 80,000 tons of tabs are disposed of each year, resulting in the waste of at least 20,000 tons of asphalt, plus the granular and filler material which are also by-products of a roofing plant.
Finally, of the new shingles which are manufactured, a certain percentage of the shingles, known as "seconds", will be of unacceptable quality. It is estimated that the amount of shingle material disposed of as "seconds" is approximately equal to the amount of shingle material disposed of as tabs.
Accordingly, there is a need to provide a method and apparatus by which old shingles and shingle material which is the by-product of the manufacture of new shingles can be recycled.
Various methods for recovering the components of discarded asphalt shingles are known in the art. One such example is found in U.S. Pat. No. 4,222,851, in which a solid extracting process is used to recover the various components. Waste asphalt shingles are shredded in a hammer mill and then passed through an extractor-desolventizer so as to form an asphalt-enriched miscella. The miscella is then subjected to evaporative techniques to separate asphalt from the solvent, and the solid particles are further segregated into their fiber, filler, and granular component parts.
U.S. Pat. No. 4,269,693 discloses a process for recovering bitumen from waste roofing felt and the like. The cooled waste material is comminuted to a particle size of less than 5 mm, such as by using a chain flail device. The comminuted particles are then fed into a tank of water, where the dirt and stone chippings drop to the bottom of the tank while the bitumen and fibers float at or near the surface of the water where they can be skimmed off.
As can be seen, these prior art processes are complicated and time consuming and require special equipment to separate waste shingles into their component parts. Accordingly, there is a need to provide a method and apparatus for recycling waste shingles which does not require separation of the shingle material into its component parts.
The primary components of shingles--asphalt and filler material--are similar to the components comprising asphalt paving composition. Accordingly, efforts have been made to recycle waste shingle material as an additive to asphalt paving composition, whereby all of the materials comprising the shingle can be utilized without separating the shingle material into its component parts. One such effort involved shredding roofing shingles into chunks that would sometimes be as large as 4 inches by 6 inches. These chunks of shingle material were then injected into a batch plant by weighing them into the plant like recycle material. However, these efforts were largely unsuccessful because the large chunks of shingle material would not completely melt down, and consequently would not uniformly intersperse with the remainder of the asphalt mix. Also, with chunks of shingle material so large, it is difficult to maintain the asphaltic content of the mix within the close standards required by state laws. Due to the high percentage of asphalt in the roofing shingles, even slight errors in weighing the shingle material into the asphalt plant can result in relatively large errors in the asphalt content of the road material.
A further problem which has been associated with prior art efforts to recycle waste shingles concerns the difficulty in shredding shingles on a mass basis. Because of their high granular material content, shingles act like large pieces of sandpaper. Thus, a large pile of shingles tends to be nearly impossible to drag, flow, separate, or handle. Because the waste shingles tend to hang together in a mass, it has been difficult to handle and weigh a predetermined quantity of shingle material.
Accordingly, there is a need to provide a method and apparatus whereby shingles can be handled, separated, flowed, and metered rather than hanging together as a large mass.